During the screening of motion pictures, there is frequently a need for the simultaneous projection of subtitles which follow the unfolding of the film. The subtitles contain a synthesized translation of the sound track of the original film.
Generally, the film print itself is used to show the subtitles which have been placed on successive print frames. Each subtitle is in a selected language and is projected onto the screen along with the picture. The subtitle is thus inherently timed with the projection.
This system is particularly time-consuming and expensive. A substantial amount of laboratory time is required to place the subtitles on the frames, and a given print must be dedicated permanently to the selected language. A print cannot be used for other than the language of the subtitle because the subtitles are a permanent part of the film. The operation is particularly long because usually between 700 and 1200 subtitles are required in a feature-length film. Further, in the case of "protected" prints--used today in increasing numbers--it is practically impossile to use the tradiational method of burning in the subtitles.
Other subtitle techniques have been attempted. For example, one system employs a second print having subtitles only and projects the subtitles simultaneously with the original print. This system is particularly complicated because it requires two projectors, two prints of the same length, and synchronization of the two projectors, which is difficult to maintain during a single screening and particularly difficult to maintain for successive screenings.